The activation of dioxygen in biological systems is a question of great importance because of its involvement in many metabolic processes. although the mechanism of oxygen activation in heme systems such as cytochrome P450 and peroxidases is becoming quite well understood, much less is known of the corresponding mechanism for non-heme systems. Non-heme iron oxygenases are involved in the oxidative cleavage of aromatic rings (catechol 1,2-dioxygenase, 3-hydroxyanthranilate 3,4-dioxygenase, homogentisate 1,2-dioxygenase), the hydrosylation of both aliphatic aromatic hydrocarbons (methane monooxygenase, proly hydroxylase, phenylalanine hydroxylase), and the autoxidation of fatty acids (lipoxygenase). These enzymes participate in aromatic and aliphatic metabolism, collange formation, and the synthesis of neurochemicals and prostaglandins. Spectroscopic (NRM, EPR, resonance Raman, Mossbauer, EXAFS) and mechanistic studies are proposed for a number of enzymes to elucidate details of the active site structure and the mechanism of action. These include intradiol and extradiol cleaving catechol dioxygenase, benzoate 1,2-dioxygenase (an NADH-dependent arene dioxygenase), and p-hydroxypenylpyruvate dioxygenase (a ketoacid dependent oxygenase). Model complexes will be synthesized and used as models to interpret spectroscopic features of the enzymes and studied with regard to their reactivities with dioxygenase, peroxide, and related species proposed in oxygenase. Areas of particular interest are: 1) biomimetic oxidative cleavage of catechols (intradiol and extradiol), 2) use of catecholate-to-Fe(III) charge transfer bonds as a probe for iron enzymes with no intrinsic visible chromophore, 3) ligand effects on high-spin Fe(III) EPR spectra and zero field splitting parameters, 4) biomimetic monooxygenerations, 5) fatty acid autoxidation mechanisms. As in the past, the synergistic interaction of the biochemical and inorganic aspects of the proposal is important for the success of the program.